Electric distribution system and conductor thereof



Aug. 14, 1934. G. A. BURNHAM ELECTRIC DISTRIBUTION SYSTEM AND CONDUCTORTHEREOF Filed April 6, 192s Patented Aug. 14, 1934 UNITED STATES PATENTOFFICE ELECTRIC DISTRIBUTION. SYSTEM AND CONDUCTOR THEREOF chusettsApplication April 6, 1928, Serial No. 268,037

4 Claims.

This invention relates to high tension electric distribution systems andapparatus and to the conductors thereof.

When an electric switch opens up its circuit 5 under heavy loads or onshort circuit, heated vapor and flame is frequently expelled from theswitch casing. If the heated vapors or flames come in contact with thehigh tension conductors they form a sufliciently low conductingpathbetween the conductor and the switch casing or other part which is atground potential to establish' a high tension flash-over are through theconducting gas. Consequently the high tension conductors are usuallyinclosed in casings which are filled with oil or other insulatingcompound for the purpose of preventing the heated and conducting gasesfrom coming in contact with and'short-circuiting the high tension bus.The oil or insulating compound, while it is a good insulator, is highlycombustible and can burn and be the source of disastrous fires. Moreoveroil or compound insulation is also subject to other disadvantagesunnecessary to enumerate here. Be cause of the combustibility of the oiland compound, and other disadvantages thereof, I have proposed a hightension conductor which is enclosed within a metal or other casing andis embedded in an inert material which prevents access of heated gasesto the conductor and which has many advantages over oil and compoundinsulation. The preferred conductor-isolating material was a materialsuch as sandand the use of such material is disclosed in my copendingap- 35 pl ications: Serial No. 239,790, filed Dec. 13, 1927, Serial No.243,902, filed Dec. 31, 1927, Serial No.

252,185, filed Feb. 6, 1928, and Serial No. 260,843,

filed March 12, 1928 which have ev'entuated into patents numbered1,748,060, 1,859,955, 1,941,463, 40 and 1,878,107, respectively.

When a body of sand is subject to the action of an-intense electric arcthe particles of sand sometimes melt and coalesce into what is in effecta vitreous rod. The resistivity of the heated sandparticles or thevitreous rod formed is considerably lower than the resistivity of thecold sand. While this lowered resistivity may be of no particularimportance under many conditions, it may be that under some conditionsof operation, as for instance under very high potentials and wherepotential is desired to be restored to the conductor-immediately afterthe interruption of the flash-over arc, the reduction in resistivity maypermit the heated-sand to carry a material 5; amount of current-,ivhichis undesirable.

An object of the present invention is the combination of an enclosedhigh tension bus and an isolating and insulating material thereforhaving the functions of the sand of my said applications, which ischaracterized by having such a 80 high resistance when highly heatedthat it will not conduct any harmful amount of current even whensubjected to the highest present-day commercial voltages used atinstallations of this nature and preferably also by being infusableunder the heat of the flash-over arc. The best material known to me atpresent is asbestos; and a conductor contained within an inclosingcasing and embedded in a body or packing of asbestos constitutes anotherobject of this invention.

A further object is generally to improve the construction of hightension switching systems and the insulation and isolation of the hightension conductors thereof.

The figure isa diagrammatic representation partially in section, of ahigh tension distribution system including oil immersed switches and ahigh tension bus orconductor arranged in accordance with the invention.

As here shown, the high tension bus 10 comprises a bare conductorsupported on' suitable spaced insulating pillars 12, within and spacedfrom the side walls of the metal enclosing casing 14. The branch 10a ofthe bus is passed through an insulating bushing and fixed in andextended through the bottom wall of the enclosing casing and connectedwith disconnect terminals 18 at lower end of thebushing. An oil immersedelectric switch 20 is located beneath said casing and an insulatedterminal thereof has a cooperating 9o disconnect terminal 22 which isadapted to 'be connected with and disconnected from said disconnectterminal 18 by vertical movements of the switch, in a; more or lessusual manner.

In accordance with this invention the conductor casing 14 is filled withan insulating body 24 which preferably is asbestos, and the conductor 10is embedded in said insulating body. The insulating body is electricallyinsulating. It is also characterized by being non-combustible so that itwill not burn or give 01f combustible or other harmful vapors or gaseswhen subjected to a fiashover are. It is also flexible sothat it canbend with the conductor and with the enclosing casing without movingaway from protective relation with the conductor.

The insulating material, in accordance with this invention, is alsocharacterized by having such high electrical resistance when highlyheated that it will not conduct any-harmful amount of current 119 evenwhen subjected to a high difference of potential between the bus and,the enclosing casing. For instance, it has been found that asbestos hasa resistance of about '0,Q00 ohms per inch cube when at white heat. Thisresistance is too high to carry sufllcient current to maintain thetemperature of the asbestos body. The material is also characterized bybeing infusible under the action of the flash-over are so that itmaintains its original state under the action of a flash-over arc. Asstated above the best material known to me at present is asbestos.Asbestos can be obtained in either fibrous or powdered form. I prefer touse the asbestos in its fibrous form and to pack the asbestos fibrescompactly into the enclosing casing 14, and about and in intimateconnection with the high tension conductor so that there will be nolarge voids between the conductor and the casing. For certain conditionsof non-combustible electrically insulating felted as bestos fibrescontained in said casing about said conductor and occupying the spacebetween it and said casing, said fibres characterized by having anelectrical resistance which is so high when the particles are highlyheated as to inhibit the conduction of a deleterious electric current atthe voltage of said conductor, said packing filling the space betweensaid casing and said conductor so that there are no large voidstherebetween and constituting means preventing access of heated gases tosaid conductor.

2. In a high tension electric distribution system, the combination of anenclosing casing, a high tension conductor located therein and insulatedtherefrom, and means which prevents access of heated gases to saidconductor comprising a compact packing of loose felted asbestos fibresoccupying said casing and surrounding said conductor.

3. A high tension electric distribution system as defined in claim 2wherein said packing comprises asbestos fibres and particles ofnon-combustible electrically insulating granular material among theasbestos fibres.

4. In a high tension electric distribution system, the combination of anenclosing casing, a high tension bus located therein and insula edtherefrom, and a packing of felted non-combustible, electricallyinsulating asbestos fibres contained in said casing surrounding said busconstituting means which prevents access of heated gases to said bus.

GEORGE A. BURNHAM.

